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<head>
<meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Document</title>
 <script>
 var year = prompt("输入年份，判断闰年还是平年。")

 if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {

     alert("它是闰年");

 } else {
     alert("它是平年");

 }
</script>
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<body>
                        
</body>
</html>